Process for electroslag welding of circumferential joints

ABSTRACT

A method is disclosed for electroslag welding a circumferential seam. The method includes feeding a consumable electrode through a vertical stationary consumable nozzle downwardly into the seam to deposit weld metal in a metal melt pool beneath molten slag, rotating the circumferential seam as the weld metal is deposited in the metal melt pool at a speed sufficient to maintain a reasonably constant level in the metal melt pool relative to the axis of rotation of the circumferential seam, and maintaining a reasonable constant distance between the nozzle and the level in the metal melt pool, the improvement which comprises stopping the rotating circumferential seam after one complete rotation, continuing the feeding of the electrode downwardly into the seam through the vertical stationary consumable nozzle so that the level of the metal melt pool rises and consumes the nozzle thus completing a circumferential welded seam.

United States Patent [1 1 Coulter et a1.

Filed:

PROCESS FOR ELECTROSLAG WELDING OF CIRCUMFERENTIAL JOINTS Inventors:William John Coulter; Brian Anthony Graville, both of Lasalle, Quebec,Canada Dominion Bridge Company, Limited, Montreal, Quebec, Canada Jan.3, 1973 Appl. No.: 320,697

Assignee:

Foreign Application Priority Data Jan. 7, 1972 Canada 131960 u.s. Cl.219/73, 219/126 Int. Cl B23k 9/18, B23k 9/12- Field of Search 219/73,126

References Cited UNITED STATES PATENTS 10/1965 Cotterman 219/73 X 3/1969Dick 219/73 X 3/1973 McCall 219/126 X 12/1971 Wiche 219/73 I -Mar. 5,1974 Primary Examiner--C. Ll Albritton Assistant ExaminerHugh D. JaegerAttorney, Agent, or FirmFetherstonhaugh & Co. v

[57] ABSTRACT A method is disclosed for electroslag welding acircumferential seam. The method includes feeding a consumable electrodethrough a vertical stationary consumable nozzle downwardly into the seamto deposit weld metal in a metal melt pool beneath molten slag, rotatingthe circumferential seam as the weld metal is deposited in the metalmelt pool at a speed sufficient to maintain a reasonably constant levelin the metal melt pool relative to the axis of rotation of 9 Claims, 4Drawing Figures PATENTEB 51974 SHEEIIUFZ PROCESS FOR ELECTROSLAG WELDINGOF CIRCUMFERENTIAL JOINTS This invention relates to welding processessuch as electroslag welding wherein a molten pool is developed andmaintained in a circumferential seam, and more particularly to animproved process for depositing weld metal in a circumferential sealparticularly by electroslag welding. The weld'able metals used includesuch materials as steel, ferrous alloys of many types, aluminum and itsalloys, copper and copper base alloys and the like.

In making a circumferential weld between workpieces, for'example partsof a pressure vessel, by the electroslag method of welding, theworkpieces are rotated in relation to the welding head until the initialportion of the weld returns to the welding zone as the final part of theweld is made. In order to complete the circumferential weld, therotation of the workpiecesis stopped and the welding head is raised sothat the electroslag welding pool fills in the remaining portion ofcircumferential seam and extends upwards in what is known as a runofftab.

The welding head has at least one nozzle for feeding a consumableelectrode into the electroslag welding pool. Flux is added to theelectroslag pool either in granular form or by use of a flux cored wireto provide a bath of molten slag above a melt pool. In conventionalelectroslag welding machines the nozzle is generally curved, that is tosay it has a 90 bend from the horizontal to the vertical, and may becooled by water. The electroslag pool is kept in place for acircumferential weld by shoes on the inside and outside of thecircumference which form dams'to contain the pool.Two types of shoes areavailable. The first is the sliding type. This provides a shoe on theinside and outside of the workpieces which is connected to the weldinghead, thus as the welding head is stationaryand the workpieces rotate,the electroslag pool is always confined by the sliding shoes- Anothertype of shoe is the leapfrog type. In this case a series of shoes areattached to the inside and outside of the workpiece across thecircumferential seam and are leapfrogged as the workpiece rotates sothat the electroslag pool is always confined by shoes acting as dams.Both the sliding shoes and the leapfrog shoes are water cooled. Whensteel is being welded the shoes are generally made of copper for ease ofcooling. It has been found that if the welding head has a curved nozzle,leapfrog shoes are very difficult to use and in genera] are impracticalas the horizontal portion of the nozzle hingers the leapfrogging of theshoes. Therefore, with a curved nozzle sliding shoes are generally used.Sliding shoes, however, have one disadvantage and that is that the innerand outer surfaces of the workpieces adjacent to the seam must bemachined or ground smooth, otherwise leaks occur from the electroslagpool and leaks in the electroslag pool can cause faults to occur in theweld due to the dropping in the level of the electroslag pool. s

It is an object of the present invention to provide a method of making aweld in a circumferential seam which does not require the raising of thewelding head after the weld has been completed.

It is anotherobject of the present invention to provide a method ofmaking a weld in a circumferential seam which may use reasonably largeleapfrog type shoes on the outside of the seam. 1

According to the present invention there is provided in a method ofdepositing weld metal in a circumferential seam, which includes feedinga comsumable electrode through a vertical stationary consumable nozzledownwardly into the seam to deposit weld metal in a metal melt poolbeneath molten slag, rotating the circumferential seam as the weld metalis deposited in the metal melt pool at a speed sufficient to maintain areasonably constant level in the metal melt pool relative to the axis ofrotation of the circumferential seam, and maintaining a reasonablyconstant distance between the nozzle and the level in the metal meltpool, the improvement which comprises stopping the rotatingcircumferential seam after one complete rotation, continuing the feedingof the electrode downwardly into the seam through the verticalstationary consumable nozzle so that the level of the metal melt poolrises and consumes the nozzle thus completing a circumferential weldedseam.

In drawing which illustrate embodiments of the invention,

FIGS. 1, 2 and 3 illustrate diagrammatically and in sequence the formingof a weld in a circumferential seam.

FIG. 4 illustrates a longitudinal cross-section through a tip of anozzle of the type used in the present invention.

The equipment required for electroslag welding according to the presentinvention includes a power source having a variable voltage control, andwire feed motors having variable speed control capable of driving feedrolls for feeding a consumable electrode to a nozzle which has'a tiplocated directly above the electroslag pool. A pair of rotating rollersis required for rotating the workpieces at a constant speed. The rollershave infinitely variable speed to adjust for the required welding speed.The speed of the rollers determines the circumferential speed of theworkpiece, which is the welding speed. In the case of large diametersthe welding speed is around a half an inch per minute, therefore therotational speed of the workpieces is small.

Referring now to the drawings, the process of the inventionv involveswelding together, the endsof two workpieces such as pipes or cylindershaving a large diameter. The end 10 of one of the workpieces 'appears inFIGS. 1 to 3. The workpieces are setup with a predetermined distancebetween the ends and are aligned axially on the rollers which rotate theworkpieces during welding. The alignment of the ends of the workpiecesis generally maintained by welding a number of plates around thecircumferential seam. The gap between the ends of the workpieces ispreferably between 1 /sinches and l fliinch and is maintained by thewelded plates, sometimes referred to as strongbacks. A special startingblock 11 is positioned in the range from the horizontal plane throughthe cylindrical axis of the angle is 1 l /2, whereas with 4 ft. insidediameter and 6 ins. thick, the preferred angle is 20.

At least one consumable nozzle 12 is positioned so that the tip 13 is apredetermined distance above the top of the starting piece 11, and alsoso that the tip 13 of the nozzle 12 comes in the centre of the startingpiece 11 between the inner and outer face of the workpiece. Thepreferred distance between the tip 13 of the nozzle 12 and the surfaceof the molten slag is maintained between approximately 1 /2 and 2 ins.If thick material is being welded then several nozzles are used. It ispreferable to use one nozzle for approximately every 2 inches of plate.For example, a 6 inch plate requires three nozzles. A consumableelectrode 14 is shown leaving the tip 13 of the nozzle 12. Internalshoes 13 are attached to the inner face of the workpieces, and externalleapfrog shoes 16 are attached to the outer face of the workpieces sothat a boundary is formed surrounding the starting piece 11. Theinternal shoes may be of any type. For large diameter cylinders it ispreferred to have leapfrog shoes as these have been found to be moreeconomical than other types. In small diameter cylinders, a continuousshoe extending around the complete circumference is preferred.

The rotational speed of the workpieces are determined by results. If theweld is laid down too fast, a poor weld occurs which has cracks in theweld. It is preferred to weld at an approximate speed of one half aninch per minute. Beyond this speed, cracking may occur in the weld.Knowing the speed of welding, it is a simple matter for one skilledin-the art to calculate the speed of rotation of the workpieces and therollers. It is also a simple matter to calculate the rate of feeding theconsumable electrode to the metal melt pool, as the size of the pool tobe filled can be calculated knowing the thickness of the workpieces andthe distance between the two ends. The voltage of the power sourceadjusts the width of the weld. If the voltage is too low, the weld lacksfusion between the weld and the original material. If the voltage is toohigh, excessive fusion may occur and the slag and molten metal can runout at the edge of the shoe. The process is started by arcing theelectrode onto the steel starting piece 11 and then adding flux. Theexact formation of the fluxes is proprietry but may be obtained from thecompanies involved in producingwelding equipment. The flux generallyincludes mixtures of metal oxides such as alumina, silica, magnesia,etc., and calcium fluoride. When molten the flux conducts electricity.The flux melts very shortly after arcing commencesto form molten slagand within a few seconds the arc is extinguished and stable electroslagconditions are established. Areing may be facilitated by inserting asmall ball of steel wool between the electrode and the starting block 11before the current is turned on.

been found that it is possible to judge when to add more flux bylistening to the sound of the operation. When the noise level rises,more flux must be added. Thus the preferred distance between the tip ofthe nozzle and the surface of the metal melt pool is in the range offrom Y 2 V2 to 3 B inches. If the rotation of the workpieces is stopped,or if the. current'stops there is poor fusion when the weld recommences,which later has to be gouged out and rewelded. The leapfrog shoes, whichare preferably copper, are attached to the outside face of the workpieceacross the seam and are water cooled. The inside shoes are attached tothe inside face of the workpieces. In the case of steel or ferrous alloyworkpieces, the shoes are attached by mild steel clips tack welded tothe workpieces orby other similar means.

As seen in FIG. 2 the metal melt pool 17 solidifies to form a weldedseam 18 as the rotation of the workpieces continue. After approximatelyhalf the seam has been welded, the start of the weld is gouged back toapproximately tangential to the inner circumference of the workpieces,thus leaving a finished line 19 which is used for the run-off to finishthe seam.

Immediately after welding, the cooled portion of the seam may bevisually examined for cracks and lack of fusion. The parameters of thewelding step may be adjusted to ensure the required parameters are met.Examination by X-ray cannot be carried out during the time the workpiecerotates on the rollers, and any manual repairs due to lack of fusion orcracks in the weld must becarried out after the circumferential weld iscompleted, and subsequently filled in by electric are welding generallymanual welding.

When the rotation of the workpieces reach the position that the gougeline 19 is vertical as shown in FIG. 3, the rotation of the workpiecesis stopped. However, the consumable electrode 14 is still fed throughthe nozzle 12, and thus the metal melt pool 17 slowly rises consumingthe nozzle 12 as the level is raised. To contain the metal melt pool 17as the level rises, a special run-off tab 20 is attachedto the frontface of the workpieces with an inside block 21 also attached to thefront face of the workpieces. The run-off tab 20 and the inside block 21conbining to contain the metal melt pool as the level rises above theouter circumference of the workpieces. When the metal melt pool reachesa high point so that it is no longer welding on the circumference of theworkpieces, the electrode-feed is stopped, and the welding current isturned off. After the seam has cooled, the portion of the run-offextending beyond the outer circumference of the workpieces is removed bygouging or burning so the completed seam has a smooth surfacesubstantially following theline of the outer circumference of theworkpieces.

Once the arc is sparked, the consumable electrode is fed through thenozzle 12 until a metal melt pool is formed beneath the molten slag,then the rotation of the workpieces is commenced and the feed of theconsumable electrode is adjusted so that the level of the metal poolremains the same throughout the rotation of the workpieces. The depth ofthe molten slag above the metal melt pool is preferably in the order ofl to 1 /2 inches, and the depth of the metal melt pool is preferablyless than 1 inch. Flux is added intermittently throughout thecircumferential weld to-maintain the depth of the molten slag asconstant as possible. It has The nozzle 30 as shown in FIG. 4 isspecially treated by having a counter bore 31 from its tip 32. Thecounter bore 31 has a larger diameter than the regular bore 33 of thenozzle 30. The reason for the counter bore 31 is to reduce the effect ofspatter from the slag which otherwise tends to allow a slag build-up onthe tip of the nozzle interfering with the feeding of the wire to themetal melt pool. For the short distance that the metal melt pool risesin the run-off, the nozzle is being consumed, and the spatter problemdoes not exist.

The welding head remains stationary throughout the welding of thecomplete circumferential seam. During the rotation ofthe workpieces, thelevel of the metal melt pool remains constant relative to the weldinghead. The only time the level of the melt pool rises is welding therun-off at the end of the operation when the nozzle is consumed. Whilethe workpieces rotate, the distance between the tip 13 of the nozzle 12and the level of the metal melt pool 17 remain constant. If the distancevaries, then the speed of electrode feed through the nozzle 12 isincreased or decreased so that the level of the metal melt pool 17 risesor falls, and the tip of the nozzle always remains at a constantdistance from the top of the metal melt pool 17.

In a preferred embodiment, a thermocouple (not shown) is attached to thetip 13 of the nozzle 12. The thermocouple produces a temperature readingwhich is interpolated to the distance between the tip 13 of the nozzle12 and the top of the metal melt pool 17. If the temperature is high itmeans the level of the metal melt pool is too close to the tip of thenozzle, if the temperature is low the level of the metal melt pool istoo far from the tip of the nozzle. Thus a thermocouple indicator canadvise an operator whether or not he should vary the feed of theconsumable electrode to the nozzle. Alternatively, this may becontrolled by electronics and the feed speed can be varied so that thistemperature remains constant and the space between the tip of the nozzleand the metal melt pool is constant.

Another method of measuring the distance between the nozzleand the metalmelt pool is by an austenitic steel dip stick. This is a manual'methodand requires a certainamount of skill from an operator. I

The vertical nozzle allows the welding to be carried out with'the metalmelt pool preferably located at a preferred angle below the horizontalplane through the cylindrical axis. The consumable electrode is fed tothe centre of the metal melt pool and this gives more room to gauge thedistance between the tip of the nozzle. and the level of the metal meltpool than the more conventional curved nozzles. It also has theadvantage of allowing outside shoes to be leapfrogged well in advanceof'the metal melt pool relative to the rotating workpieces.

EXAMPLE In a specific example of this process, two mild carbon steelcylinders having an inside diameter of 47 inches and a wall thickness of2 inches were circumferentially welded together. One nozzle was used forthe weld having an outside diameter of five-eighths in. The diameter ofthe consumable electrode wire was one-eighth in. and the end of thenozzle was drilled out to an internal diameter of seven thirty-secondthsin. for a distance of 5 inches.

The welding speed was five-eighths in. per minute with a welding currentof 600 amps at 40 volts. The resulting weld was radiographed, sectionswere cut out and examined and the joint was shown to be free from alldefects. I

The embodiments of the invention in which an exclusive property orprivilege-is claimed are defined as follows: l I 1 1. In a method ofdepositing weld metal in a circumferential seam, which includes feedinga consumable electrode through a vertical stationary consumable nozzledownwardly into the seam to deposit weld metal in a metal melt poolbeneath molten slag, rotating the circumferential seam as the weld metalis deposited in the metal melt pool at a speed sufficient to maintain areasonably constant level in the metal melt pool relative to the axis ofrotation of the circumferential seam andmaintaining a reasonablyconstant distance between the nozzle and the level in the metal meltpool, the improvement which comprises stopping the rotatingcircumferential seam after one complete rotation, continuing the feedingof the electrode downwardly into the seam through the verticalstationary consumable nozzle so that the level of the metal melt poolrises and consumes the nozzle thus completing a circumferential weldedseam.

2. The method of depositing weld metal in accordance with claim 1wherein the constant levelin the metal melt pool is maintained at thecircumferential seam in the range from the horizontal plane through thecylindrical axis of 30 below the' horizontal plane.

3. The method of depositing weld metal in accordance with claim 1wherein the constant level in the metal melt pool is maintained at thecircumferential seam at an angle 0 below the horizontal, where 0 isdetermined from the formula Cos. 6 D/D T/2, where D is the insidediameter of a workpiece having the circumferential seamtherein, and T isthe wall thickness of the workpiece.

4. The method of depositing weld metal in accordance with claim 3wherein the reasonably constant distance is maintained between thenozzle and the level in the metal melt pool by sensing the temperatureof the metal meltpool fromthe nozzle, comparing the temperature with apredetermined value and adjusting the speed of feeding the consumableelectrode to deposit weld metal in the metal melt pool as necessary sothe distance between the nozzle and the level of the metal melt pool issufficient to maintain the temperature at the predetermined value.

5. The method of depositing weld metal in accordance with claims 1wherein the distance between the nozzle and the level of the metal meltpool is in the range of from 2 to 3 /2 inches. I

6. The method of depositing weld metal in accordance with claim 1wherein individual welding shoes are leapfrogged on the outside surfacesof the circumferential seam and at least one welding shoe is provided onthe inside surfaces so that the melt pool is always contained.

7. The method of depositing weld metal in accordance with claim 1wherein the circumferential seam is rotated at approximately one halfinch per minute.

8. The method of depositing weld metal in accordance with claim 1wherein the consumable nozzle has a tip which is counter bored to adiameter greater than the regular bore.

9. The method of depositing weld metal in accordance with claim 1wherein one consumable nozzle is provided for every 2 inch thickness ofa workpiece having the circumferential seam therein.

1. In a method of depositing weld metal in a circumferential seam, whichincludes feeding a consumable electrode through a vertical stationaryconsumable nozzle downwardly into the seam to deposit weld metal in ametal melt pool beneath molten slag, rotating the circumferential seamas the weld metal is deposited in the metal melt pool at a speedsufficient to maintain a reasonably constant level in the metal meltpool relative to the axis of rotation of the circumferential seam andmaintaining a reasonably constant distance between the nozzle and thelevel in the metal melt pool, the improvement which comprises stoppingthe rotating circumferential seam after one complete rotation,continuing the feeding of the electrode downwardly into the seam throughthe vertical stationary consumable nozzle so that the level of the metalmelt pool rises and consumes the nozzle thus completing acircumferential welded seam.
 2. The method of depositing weld metal inaccordance with claim 1 wherein the constant level in the metal meltpool is maintained at the circumferential seam in the range from thehorizontal plane through the cylindrical axis of 30* below thehorizontal plane.
 3. The method of depositing weld metal in accordancewith claim 1 wherein the constant level in the metal melt pool ismaintained at the circumferential seam at an angle theta below thehorizontal, where theta is determined from the formula Cos. theta D/D +T/2, where D is the inside diameter of a workpiece having thecircumferential seam therein, and T is the wall thickness of theworkpiece.
 4. The method of depositing weld metal in accordance withclaim 3 wherein the reasonably constant distance is maintained betweenthe nozzle and the level in the metal melt pool by sensing thetemperature of the metal melt pool from the nozzle, comparing thetemperature with a predetermined value and adjusting the speed offeeding the consumable electrode to deposit weld metal in the metal meltpool as necessary so the distance between the nozzle and the level ofthe metal melt pool is sufficient to maintain the temperature at thepredetermined value.
 5. The method of depositing weld metal inaccordance with claims 1 wherein the distance between the nozzle and thelevel of the metal melt pool is in the range of from 2 1/2 to 3 1/2inches.
 6. The method of depositing weld metal in accordance with claim1 wherein individual welding shoes are leapfrogged on the outsidesurfaces of the circumferential seam and at least one welding shoe isprovided on the inside surfaces so that the melt pool is alwayscontained.
 7. The method of depositing weld metal in accordance withclaim 1 wherein the circumferential seam is rotated at approximately onehalf inch per minute.
 8. The method of depositing weld metal inaccordance with claim 1 wherein the consumable nozzle has a tip which iscounter bored to a diameter greater than the regular bore.
 9. The methodof depositing weld metal in accordance with claim 1 wherein oneconsumable nozzle is provided for every 2 inch thickness of a workpiecehaving the circumferential seam therein.